The following U.S. patent publications are also noted and hereby incorporated by reference for their teachings: US 20040114631 by Aiken et al., published Jun. 17, 2004, and 20040100938 by Aiken et al., and published May 27, 2004, both of which are directed to the wireless remote control of locomotives; and 20030151520 by Kraeling et al., published Aug. 14, 2003, and teaching a rail yard remote control system for locomotives.
The railroad industry, through the Association of American Railroads (AAR) has obtained the right to use radio spectrum in the 220 MHz band for remote locomotive control. The frequency allocation consists of at least two two-way radio channels. These channels are cleared nationwide and will be used for the Remote Control Locomotive (RCL) application. Additional channel pairs in the 220 MHz band may be used at specific locations where individual licenses have been obtained.
Coexistence of RCL systems within the same block of spectrum will require a coordinated, standard method for accessing the channel(s) within the spectrum block. This is paramount to implementations in the 220 MHz band because of the very limited availability of expensive, licensed spectrum. Due to this limited number of radio channels, railroads operating in the same area may be forced to use common channels and share the repeater infrastructure. Therefore, a prime motivator for an open protocol is interoperability among user railroads and among vendors. These two dimensions of interoperability are required to maximize efficient use of limited spectrum available for this application. Vendor interoperability in this context extends down to the system level. As used herein, the term system is intended to reflect at least a single controlled locomotive (locomotive control unit; LCU) and its associated controlling devices (operating control units; OCUs). In other words, it is not anticipated that a locomotive unit would be required to operate with a controller unit from a different vendor. By ruling out this level of interoperability, the open protocol need not define message content or other details of the interactions between locomotive and controller units. This not only simplifies the specification, but also leaves room for vendor differentiation and innovation.
Contemplated in the present invention are systems and methods for not only reliable remote-control communications, but use of repeaters and communications servers to assure reliable, centralized communication between locomotives and operator control units. In another embodiment, there is described a reliable distributed communication mode using an uncorrelated time sequence that does not interfere with a time division multiple access network. Differentiation between the centralized mode and the distributed mode is accomplished by assessing whether a locomotive and control unit is within a rail yard's infrastructure. Moreover, reliability is assured by using a coordination server that dynamically routes packets between multiple satellite RCL repeaters based on received signal strength. Lastly, the present invention further contemplates the use of an out-of-band transmission to upgrade and test operator control units, thereby allowing for field maintenance and software upgrades.
All RCL systems deployed by a railroad, regardless of supplier, should be able to utilize a common, shared wireless infrastructure. Currently envisioned components of this infrastructure include repeaters and coordination servers. Shared use of a repeater will require use of a Common Air Interface (CAI), common system functions, and a standard message set for communication with a local configuration server.
The Common Air Interface (CAI) defines a reference point at which communications between radios can take place. In one embodiment of the present invention, this assumes that communications through the reference point are done at a gross bit rate of 9600 bps in a 12.5 kHz channel. In accordance with an aspect of the present invention, communication within an RCL system is based on the LCU and each OCU transmitting once a second at the proper time on a specific assigned frequency in the 220 MHz band. Listeners receive the transmitted message by receiving at the same time each message is transmitted.
In order to achieve reliable shared use of the assigned frequency, disclosed in embodiments herein there is described a scheme whereby each device using the frequency will know exactly when to transmit. This type of scheme is known as Time Division Multiple Access (TDMA). TDMA requires that a fixed period of time be divided into time intervals reserved specifically for transmissions from individual devices (e.g. OCUs or LCUs). For example, the time division multiple access proposed for RCL communications protocol provides multiple access to a radio frequency (RF) channel in the time domain.
In accordance with another aspect of the present invention, and as illustrated in detail below relative to FIG. 6, a repeating one second frame is divided into multiple time slots, with slots assigned to individual systems—one for the locomotive controller unit (LCU), and one for each of two operator control unit (OCUs). The basic TDMA frame for the RCL CAI repeats every second. This frame is divided into sub-slots that will be used by individual devices for their transmitted packet.
An RCL repeater, where used, is generally intended to include a fixed radio device that serves to increase the reliable range of operation of RCL Systems. The RCL repeater does this by re-transmitting radio transmissions it receives from LCUs and OCUs. Advantages achieved as a result of the use of a repeater include optimum antenna placement and elevation, extended coverage area, and avoidance of obstacles in the direct RF path between OCU and LCU. In the AAR specification, each unit must specifically direct its message to either a repeater or a peer device. Furthermore, the frequency pair is considered a channel. It consists of the repeater transmit frequency (the B frequency), and the LCU/OCU receive/transmit frequency (the M frequency). The basic function of an RCL Repeater is to receive transmissions on the M frequency of the channel, and, retransmit them on the B frequency of the channel. The RCL repeater will also process messages as an Repeater Coordination Server (RCS) when multiple repeaters are used in a yard.
A Repeater Coordination Server (RCS), where used, is a process/system that implements the logic necessary to coordinate the communications of multiple repeaters and RCL Systems in an RCL operation. Embodiments of the present invention contemplate multiple RCL Systems using repeaters controlled by an RCS. The RCS coordinates the operation of multiple repeaters by dynamically routing repeater transmissions. The physical configuration of some yards may make it necessary to install multiple repeaters. In this situation the RCS will provide message routing and slot synchronization among the repeaters.
There are two modes in which channel and time slot usage is coordinated between RCL systems utilizing the RCL common air interface, Distributed and Centralized. Each mode utilizes the TDMA frame structure described above.
As will be further described relative to FIG. 2 below, an RCL system operates in Distributed Coordination Mode (DCM) when it is not in coverage of available repeater infrastructure. This mode is generally applicable where RCL demand is light or OCUs and LCUs are capable of reliable communications without repeaters. Typical locations for DCM operation are in small yards or industries along the railroad line. In DCM, individual RCL system devices contend for and self-regulate shared usage of available radio channels.
An RCL system operates in Centralized Coordination Mode (CCM) when its LCU and OCU devices communicate directly or via Repeaters in slots coordinated by the Repeater infrastructure. This is the default mode of operation when infrastructure is available. The Repeater infrastructure provides expanded communications coverage as well as broadcast information about channel and time slot availability for use by initializing RCL systems. By monitoring the repeater's broadcast transmissions during initialization, an RCL system can intelligently choose a channel and time slot that will be free of interference from other operating RCL systems.
In situations where the concentration or frequency of RCL activity does not justify coordinated repeater infrastructure, RCL systems will operate in Distributed Coordination Mode (DCM). DCM operation can be used anywhere and should therefore be restricted to the two nationwide channels. In DCM, the LCU and OCUs communicate directly with one another.
In accordance with the present invention, there is provided, a system and method for remote control of locomotives, comprising: a highly reliable time division multiple access network; at least one locomotive equipped so as to be operatively controlled by a locomotive control unit (LCU) suitable for transmitting and receiving information via the network; at least one operator control unit (OCU) suitable for transmitting and receiving information via the network, wherein the LCU and OCU each device will only transmit in a defined period of time; and said network employing both spatial and frequency diversity for remote control using repeater infrastructure, wherein said network further comprises an Repeater Coordination Server (RCS) to implement logic to coordinate the communications of multiple repeaters and RCL Systems and where said RCS will include at least one repeater to provide spatial diversity in that the path to any mobile or portable unit (LCU or OCU) is different for each repeater, and each time the repeater receives a message from an LCU or OCU, it calculates a rating for the message integrity (Received Signal Strength Indication; RSSI) and sends the message and rating to the RCS using an Inter-Access Point Protocol (IAPP) over an off-channel backhaul link where the message is stored, the RCS using the stored message information to determine which repeater has a best path to the destination unit for the current message, and forwards the message to this repeater for retransmission.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.